Pig influenza 'barely monitored'

The 2009 pandemic influenza virus, H1N1, may not be under sufficient surveillance in pigs to prevent new and more deadly strains emerging, public health experts have warned.

The lack of surveillance means the virus is more likely to continue to circulate between humans and pigs, making further mutations more likely.

Animal health organisations are cautious about too keen a focus on pigs, fearing an overreaction including mass culling of pigs, as happened in Egypt. Trade bans on pigs and pork are another outcome governments would like to avoid.

Bernard Vallat, director-general of the World Organisation for Animal Health (OIE) made a statement just minutes after the World Health Organisation (WHO) declared swine flu a pandemic on June 11.

He said the role of animals had not so far been demonstrated in either the spread or development of the virus.

"So far the role of animals has not been demonstrated in the virus's epidemiology or spread," he asserted.

Others say, however, that H1N1 may in fact be the product of minimal flu surveillance in pigs in the years prior to the emergence of the pandemic.

Hong Kong University flu geneticist Gavin Smith and colleagues said in a recent report that lack of systematic swine surveillance allowed for the undetected persistence and evolution of this potentially pandemic strain for many years.

Smith says pigs have played an "obvious" role in the epidemiology of swine flu. He also says it is possible that H1N1 has been circulating between pigs and humans for many years.

So far, only pigs in Alberta, Canada, have been found to host the pandemic strain of the virus. No-one knows how the herd became infected.

UK laboratories have demonstrated that pigs can easily become infected with the virus, and readily transmit it between themselves and shed it into the environment.

Jimmy Smith, head of livestock affairs at the World Bank in Washington DC, and a member of the organsation's flu task force said it was highly likely that more pigs were infected in more places than just the one Canadian pig farm.

And OIE-FAO animal flu (OFFLU) expert Steve Edwards says that just because there is no evidence to support the role of pigs in swine flu, does not mean that they do not play a role.

Pigs have been far less the focus of laboratory networks like Edwards', however, which have tended to focus on surveillance of influenza viruses in poultry and wild birds, with pigs low on the agenda.

Fears over the next pandemic influenza strain have traditionally focused around the avian H5N1 flu virus, which leads to serious disease in poultry and causes huge economic losses.

Any outbreaks must be reported in poultry or other birds, but similar requirements are not in place for pigs. States may now voluntarily report influenza in pigs, OIE says.

OFFLU says it has had only a limited response to suggestions that countries share information on swine flu, which is usually seen as a farming problems, and sequence any recent samples for genetic analysis.